Heterogeneous TAG-72 and CEA expression has been observed in a variety of human carcinomas. The presence of antigen negative tumor cells is an important consideration when designing clinical protocols which rely on monoclonal antibody binding for either diagnosis or therapy. We identified agents capable of altering cellular differentiation which can upregulate the expression of tumor antigens. We are studying the regulation of CEA expression in a variety of human colon carcinoma cells following interferon treatment. The most dramatic increase in CEA expression and related mRNA transcripts was observed in moderately differentiated colon tumor cells. IFN-gamma also increases CEA secretion from highly differentiated colon tumor cells without any dramatic increase in cell-associated CEA expression. Serum samples from patients diagnosed with different adenocarcinomas and treated with recombinant interferon were analyzed retrospectively for changes in circulating TAG-72 and CEA levels. The results indicate that interferon treatment can substantially increase circulating blood levels of TAG-72 and/or CEA in approximately 65% of the cases. Furthermore, interferon does not cause the appearance of either tumor antigen in the serum of patients diagnosed with nonadenocarcinomas. These preliminary results indicate that interferon may be an important addition for more sensitive serum assays for the detection of these human tumor antigens. Several human colon carcinoma cell types do not express higher levels of CEA following interferon treatment. However, IFN-gamma treatment does induce higher levels of 2'-5'-oligoadenylate synthetase [2'-5' (A)] activity indicating the existence of separate pathways for antigen expression and 2'-5' (A) activity. In addition, treatment of those same cells with analogues of cyclic AMP did increase CEA as well as CEA-related mRNA transcripts. Thus, multiple cellular pathways exist by which differentiation-inducing agents, such as interferon and cyclic AMP, can regulate human tumor antigen expression.